Summary

High-temperature superconductors are complex and brittle ceramics that can conduct electrons without the least bit of electrical friction if they are chilled to temperatures of about 175 degrees below freezing--positively balmy compared to the frigid conditions that metals require to perform this feat. But heat one up a bit, and the physics gets downright strange: Their electrical and magnetic properties no longer resemble those of metals, other ceramics, or any other known materials. In this so-called normal state, these copper-oxide-based materials, known as cuprates, behave like good metallic conductors in some ways, while in others like nonconducting insulators. The eventual theory of these materials will have to explain this strangeness.